There exists an ever increasing demand for power dissipation schemes for electronic circuits. Circuits used in fields such as industrial motor control, power supplies for computers, electric vehicles, etc. tend to be very high power and require efficient heat dissipation means. In the past, one approach for dissipating a great deal of heat from electronic circuits has been to use a liquid cooling scheme whereby the electronic circuit is mounted to a heatsink apparatus which has liquid flowing through it.
In the past, it has been very expensive and difficult to fabricate an effective heatsink apparatus. For example, the prior liquid cooled heatsinks have been machined as two separate parts. The two parts are welded or brazed together to form a cavity through which liquid flows. The electronic circuit would typically be laid out on a substrate which would be soldered to the heatsink. Such a configuration gives rise to many disadvantages.
For example, with a typical metal liquid cooled structure comprised of two welded or brazed halves, with a meandering channel enclosed within, there is an inherent problem with corrosion of the welded or brazed joint. Attempts have been made to plate the inside of the channel or line it with metal foils that have good corrosion properties. Alternatively, copper tubing shaped and embedded in an aluminum plate has been used. The described prior fabrication methods require expensive machining, are labor intensive, and do not provide the optimal cooling environment for high power circuits.
Another disadvantage of prior schemes is their weight. For applications such as electric vehicles or electric trains, the power electronics comprise a substantial portion of the motor driver. Reduction and weight of these components translates to energy savings. Conventional liquid cooled power modules, since they are made of metal or metal alloys, are inherently very heavy.
Another important disadvantage of conventional liquid cooled modules is their reliability. Ceramic isolation substrates which support the circuit must be soldered onto the metal liquid cooled baseplates. The process has two disadvantages, thermal mismatch and voiding. The thermal mismatch is typically between 10-12 ppm/.degree. C. This leads to high strains and stresses during any type of thermal cycling. Solder fatigue and crack propagation can lead to cracks running the entire lateral length of a solder joint.
Furthermore, soldering large areas is generally difficult and often leaves large voids randomly located under the substrate. The implication of both thermal mismatch and voiding is poor heat transfer and therefore poor performance and reliability.
Consequently, what is needed is a power dissipation apparatus which avoids the disadvantages of expensive fabrication, cumbersome weight, thermal mismatch, voiding and reduced performance and reliability.